Autotrophic Nutrition: Photosynthesis and Chemosynthesis

len Alfred Ajibola - Sat, 25th May, 2019 @ 7:11 PM

Topics in Biology

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Academic Questions in Biology

Please click here to see all Questions and Answers

In a food chain, the primary consumers are classified under trophic level  _____.

  • A. Zero

  • B. One

  • C. Two

  • D. Three

  • E. Four

  • F. Five

Cold blooded animals are referred to as _____.

  • A. Homeotherms

  • B. Endotherms

  • C. Poilokitherms

  • D. Ectotherms

  • E. Thermotherms

  • F. None of the above

All reptiles are vertebrates.

  • A. True

  • B. False

_____ cells are responsible for the formation of osteoblasts.

  • A. Osteocytes
  • B. Chondrocytes
  • C. Chondroblasts
  • D. Osteoclasts
  • E. Osteoprogenitor cells
  • F. Osteoblastic

_____ is a bone that constitute the axial skeleton.

  • A. Clavicle
  • B. Scapula
  • C. Patella
  • D. Radius
  • E. Sternum
  • F. Femur

Which of the following is false concerning cartilages and bones?

  • A. Cartilage does not have a direct blood supply while bones have direct blood supply
  • B. The process of ossification replaces a cartilage to bone
  • C. The protein that makes up cartilage is called chondrin while that that makes up bone is called ossein
  • D. Cartilage grows from both ends while bones grow from one of its epiphysis
  • E. They both have living cells within them
  • F. Haversian system is absent in cartilage but present in bones

A diagram showing the movement of energy through a food chain is called a _____.

  • A. Food Chain
  • B. Food Web
  • C. Food Energy
  • D. Food Link
  • E. Food Flow
  • F. Food Pyramid

Which of the following is NOT a part of the wrist bones (or carpal bones)?

  • A. Cuboid
  • B. Scaphoid
  • C. Hamate
  • D. Triquetral
  • E. Pisiform
  • F. Trapezium

Autotrophic Nutrition:

One of the characteristics of living organisms is their ability to feed. This process of feeding is what nutrition entails. In fact, nutrition is one of the basic characteristics of life.

Please read more on the basic characteristics of life here.

Nutrition can be defined as the intake of food or nutrients by living organisms, to be used for growth and every other processes required for the orgnism's survival.

Regarding nutrition, an organism will either manufacture its own food or depend on ready-made food. For this reason, the mode of nutrition can be grouped into two major classes. These are:

  1. Autotrophic nutrition

  2. Heterotrophic nutrition

In this article, we will explain the processes involved in autotrophic mode of nutrition.


Autotrophic mode of Nutrition

In autotrophic nutrition, organisms are able to manufacture or produce their own food. In this regard, organisms that manufacture their own food are referred to as autotrophs.

Autotrophic nutrition can be put into two types. These are:

  • Photosynthetic nutrition

In photosynthetic nutrition, organisms manufacture their food by utilizing carbon(IV)oxide (CO2) and water (H2O) in the presence of sunlight. This process is termed photosynthesis and all green plants photosynthesize.

Photosynthesis is defined as a process whereby green plants manufacture sugars (food) by utilizing carbon(IV)oxide (CO2) and water (H2O) in the presence of light energy (sunlight) while giving off oxygen (O2) as a by-product.

The equation below expresses the definition of photosynthesis.

6CO2 + 6H2O -> C6H12O6 + 6O2

Please read on sugars here

Although not seen in the equation; light energy and chlorophyll are also crucial for a successful procedure of the photosynthetic reaction.

Photosynthesis occurs in a plant’s leaf. The leaves of plant contain an organelle named chloroplast. In fact, it is this chloroplast that houses the chlorophyll.

The chlorophyll gives the plant’s leaf its green coloration. Also, it is the chlorophyll that traps sunlight energy.

Note: In plants, photosynthesis and reproduction are entirely two different processes. Photosynthesis occurs in the plant's leaf while sexual reproduction in plants take place in the flower.

You can read on plants' sexual and asexual reproduction here.


How Photosynthesis works

An endothermic reaction is a reaction that absorbs heat from its surroundings. Photosynthesis is an endothermic reaction since it requires sunlight energy. Meanwhile, understand that it isn't every stage in the process of photosynthesis that requires sunlight.

You can read on the sun and solar system here.

Photosynthetic reaction is put into two stages or reaction. These are:

  1. Light stage or light reaction

  2. Dark stage or dark reaction

  • Light reaction

This stage of photosynthesis occurs in the presence of sunlight, that is; during the day. The chlorophyll present inside the chloroplast in the plant’s leaf traps the light or solar energy.

Recall that the reactants in a photosynthetic reaction are carbon(IV)oxide and water molecules (see the photosynthetic equation above). The trapped light energy is used for breaking down or splitting water molecules into hydrogen ion (H+) and hydroxyl ion (OH-).

The process of splitting water into hydrogen ion (H+) and hydroxyl ion (OH-) in the presence of sunlight is referred to as the photolysis of water. It is shown in the equation below:

4H2O -> 4H+ + 4OH-

Note: The co-enzyme NADH is reduced to NADPH during the photolysis of water. Also, ATP is formed during this process.

  • NADH means Nicotinamide Adenine Dinucleotide

  • NADPH means Nicotinamide Adenine Dinucleotide Phosphate

  • ATP means Adenosine TriPhosphate

During the photolysis of water, the formed hydroxyl ion is further oxidized into water and oxygen as shown in the equation below.

4OH- -> 2H2O + O2

The oxygen given off as a by-product of photosynthesis comes from the light stage or reaction.

The diagram below explains the light and dark stages of photosynthesis.

Photosynthesis Reactions - Len Academy

The sun is regarded as the ultimate source of energy. This is a statement of fact since the process of photosynthesis depends on solar (or sunlight energy).

Without the sun, there will be no green plants. Consequently, without green plants, there will be no animals. In short, there will be no flow of energy as seen in food chain.

Please read on food chain here.


  • Dark reaction

This stage of photosynthesis occurs in the absence of light, that is; at night.

During the dark stage, the ATP is utilized as carbon(IV)oxide is taken in through the stomata of the plant’s leaf. Meanwhile, you can think of the stomata as an opening in the plant's leaf where gases like carbon(IV)oxide and oxygen enter and exit the plant.

Carbon(IV)oxide reacts with the hydrogen ion (4H+) produced from the initial light reaction. After a series of step by step reaction, (with each step controlled by a specific enzyme); sugar (or food) is manufactured, produced or formed.

The dark reaction is shown in the equation below:

4H+ + CO2 -> C6H12O6 + H2O

Note: C6H12O6 is the chemical formula for simple sugar.

It is worthy of note to state that the sugar produced in photosynthesis occurs in the dark stage or reaction. However, all green plants, blue-green algae, spirogyra and some protists carry out photosynthesis.

Please read more on protists here.


  • Chemosynthetic Nutrition

Organisms that manufacture food in a chemosynthetic manner do not require sunlight energy, rather chemicals are utilized here.

Chemosynthetic organisms (also referred to as chemotrophs) synthesize their food from the oxidation of simple inorganic substances (chemicals) like carbon(IV)oxide (CO2), ammonia (NH3), nitrite(NO2) and water (H2O).

At the moment, you can consider oxidation as a chemical reaction that involves oxygen (O2).

Bacteria like nitrosomonas and nitrobacter make use of chemosynthesis in the manufacture of food. This is shown in the equation below:

  • Nitrosomonas will convert ammonia (NH3) to nitrite (NO2).
  • 2NH3 + 3O2 -> 2HNO3 + H2O + Energy


  • Nitrobacter converts nitrite (NO2) to nitrate (NO3).
  • HNO2 + O2 -> HNO3 + Energy

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Pufferfish contain a toxin called tetrodotoxin. This makes them foul tasting and poisonous to predators. Tetrodotoxin is about 1,200 times more poisonous than cyanide, and there is enough toxin in one pufferfish to kill 30 adult humans. Unfortunately, there isn't any known antidote to this poison.

Interestingly, a delicacy in Japan (called fugu) is made from pufferfish. This meal is very expensive, and must be prepared by trained and licensed chefs. An improper preparation of fugu may lead to the customer's death. Sadly, such deaths are recorded annually

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Robert Waldow - Len Academy

Robert Wadlow (1918–1940) remains the tallest man ever recorded in the Guinness World Records. He was an American who stood at 8 feet, 11 inches.

An abnormally enlarged pituitary gland had resulted into Robert Wadlow's giant size.

Cockroach is the fastest land animal on six legs

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Like humans, all apes laugh when tickled

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An ostrich's eye is bigger than its brain

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Slugs have four noses

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Bats aren't birds, rather, they are mammals. Infact, they are the second largest order of mammals after rodents. We have over 1,400 species of bat. Globally, they make up about 20% of all classified mammal species


For a thing to be considered living, it must possess all the basic characteristics of life. These include:

  1. Movement

  2. Respiration

  3. Nutrition

  4. Irritability or Sensitivity

  5. Growth

  6. Excretion

  7. Reproduction

  8. Death

  9. Adaptation

  10. Competition

Please read the explanations on all the basic characteristics of life here

During strenuous exercises like sprinting or running, your body may actually work in the shortage of oxygen. During this time, your body owes oxygen (called oxygen debt) and it must be replenished or repayed after the exercise is stopped. This is why you breathe excess of oxygen after you stopped the exercise.

This is the concept of anaerobic respiration

Food Chain - Len Academy

A food chain is a diagram that shows the relationship between plants and animals within a habitat on the basis of how they rely on each other for food.

Note: Habitat is a place where an organism live. It is of three types:

  • Terrestrial (Land)
  • Aquatic (Water)
  • Arboreal (Treetops)

You can read on food chain here

The term Biology originated from two Greek words. They are:

  • Bios: means life.

  • Logos: means knowledge or to study.

Biology can therefore be defined as the study of life

Anything that has life is generally considered as a living organism (or organism). All living organisms must be able to carry the following activities:

  1. Movement

  2. Respiration

  3. Nutrition

  4. Irritability or Sensitivity

  5. Growth

  6. Excretion

  7. Reproduction

  8. Death

  9. Adaptation

  10. Competition

The above listed points are often regarded as the basic characteristics of life. You can memorize them using the acronym -> MR. NIGER DAC.

You can read on the introduction to biology and the basic characteristics of life here

The gas used in the manufacture of food by plants is Carbon dioxide or Carbon(IV)oxide or CO2

Plants manufacture food through a process called photosynthesis.

Please read on photosynthesis here

It is noteworthy to state that plants are the only orgnisms that take away CO2 from the atmosphere